A drilling template is a negative blank of a recipient jaw with at least one drilling guide for positioning one or more tooth implant bores in the recipient jaw. An aesthetically pleasing implanted tooth is dependent upon proper bore placement and depth in relation to other teeth, placement in appropriate jaw bone stock and duplication of the angle of adjacent teeth in the recipient jaw, all of which must be incorporated into the drilling template. For the purposes of this application, the words “recipient jaw” refers to the teeth, gums, landmarks, supportive and ancillary structures within the area that is designated to receive an implant.
In one method for creating a drilling template known in the art, such as in Poirier, U.S. Pat. No. 5,725,376, coordinates of radio opaque markings along with a jaw image, taken with CT or MRI, are used by a CNC machine to drill holes in a negative impression of the recipient jaw. The resultant drilling template is used in drilling bores for implants in the recipient jaw. Use of a CNC machine, though, is undesirable in a clinic setting.
For the purposes of this application, “drilling template” and “negative impression” refer to physical objects utilized in the production of drilling implant bore guides. For the purposes of this application, a “model” is further defined as a physical object, such as a model of a jaw, created from a computer representation.
In a second method for creating a drilling template that, for the purpose of this application is referred to as the “boundary method”, boundary information is taken from a digital image of the recipient jaw, such as from a CT or MRI image. This digital boundary information is entered into an image processing unit and used to form a computer representation of a negative mouth impression. Drill holes are subtracted from the computer representation and the resultant data is sent to a machining process, such as a CNC Machine, to create a drilling template.
For the purposes of this application, an “image” or “digital image” refers to an image taken, for example, by a CT or MRI imaging unit that is transferred digitally to a digital processing unit.
For the purposes of this application, a “computer representation” refers to a digital image that has been processed by a digital processing unit, for example, to place drill bores within the computer representation.
A proper implant drilling template, created utilizing the boundary method, begins with creating a proper image, using CT for example, of the recipient jaw. When the recipient mouth contains metal inserts such as tooth fillings, the image produced using CT contains many artifacts that smear and/or distort the true surface boundaries of the recipient jaw. Since image artifacts are improperly removed to recreate the surface boundaries, the drilling template used to guide the drilling of tooth implant bores often provides an aesthetically displeasing implanted tooth or an unusable drilling template.
Prior art image correction software, unfortunately, relies on default settings to reconstruct the jaw image hidden by artifact distortion, a process wherein the software estimates the distorted jaw boundaries. A drilling template that is made according to this estimated jaw model may not be supported by adjacent teeth and/or may have improperly aligned drilling guides. The resultant tooth implant will be out of line with adjacent teeth or, worse, implanted into a non-supportive bone section in the recipient jaw bone.
Another problem in constructing a pleasing implanted tooth using the boundary method, occurs in properly mounting the finished drilling template on the recipient jaw area. When the teeth adjacent to the planned implants have complex concavity and/or convexity, the resultant drilling template often is difficult to mount or remove from the jaw. In the presence of such curvature complexity, imaging software will often rely on default settings to smooth out such curvatures, again yielding a drilling template with improper drilling guides and resultant aesthetically displeasing implanted teeth.
Kruger, U.S. Pat. No. 5,927,982, attempts to create a drilling template from a negative mouth impression modified using a CT scan of the recipient jaw area. The correct bore placement is identified in the CT scan and, using a multi-axis drilling platform, the negative impression is drilled. This method of drilling a negative impression is cumbersome and, worse, imprecise. As Kruger notes, the CT scan is adversely affected by “metal restorations or prostheses that will cause scatter” (column 7 line 34). This results in image aberrations that his method cannot correct, yielding a drilling template from which misaligned implant bores are drilled or an unusable drilling template.
Swaelens et al., WO 95/28688 provides an imaging method for determining muscle and tendon position that may be helpful in determining tooth implant bore location, but fails to teach how to correct surface boundaries distorted by metal inserts or correct for complicated tooth curvatures. As a result, the resultant drilling template may provide inaccurate bore placement and aesthetically displeasing results.